Tagalog is the most widely spoken tongue in the Philipines today. Nowadays it is written in a Roman alphabet, but prior to Spanish colonial rule, Tagalog speakers employed a syllabic alphabet named Baybayin to record their language.

The Tagalog Baybayin is one of the many indigenous scripts of pre-colonial Philipines The development of scripts in Philipines remains somewhat of a mystery due to destruction of native literature by Spanish authorities as well as poor preservation of the plant-based writing material in the Tropics. It is thought that scripts in Philipines derived from the Kawi script of Java around the 14th century CE. Ultimately, scripts in Philipines derive from Indian scripts. Like Indian scripts, every Tagalog letter inherently carries the vowel /a/. Furthermore, in order to represent a different vowel, diacritical marks called kudlit are added to the basic letter. In the case of Tagalog, a dot above the letter represents either /e/ or /i/, whereas a dot below represents /o/ or /u/.

The following is the basic Tagalog script:

The following are the vowel diacritics:

Originally the Baybayin did not represent consonants occuring at the end of the syllable, even though the syllabic structure of Tagalog does allow an ending consonant.

During the 17th century CE, in order to more fully represent Spanish loanwords, especially those used to translate the Bible, the Spanish priest Father Francisco López introduced a new kudlit in the form of the plus sign or cross (+) which if placed under a letter that removes the vowel.